[fset-devel] FSet on ABCL

[Joshua TAYLOR]

On Wed, Oct 26, 2011 at 5:41 PM, Scott L. Burson <Scott at sympoiesis.com> wrote:
> On Wed, Oct 26, 2011 at 10:12 AM, Alessio Stalla
> <alessiostalla at gmail.com> wrote:
>> I don't think a symbol for which there is no special declaration in
>> scope can be considered to name a dynamic variable, and thus to have a
>> value cell at all.
>
> On a strict reading, you're probably correct.  But I had never seen an
> implementation for which this was not the case.

I'm not sure a strict reading would have that. Symbols can have value
attributes, and value attributes are accessed by symbol-value [1]:
"If a symbol has a value attribute, it is said to be bound, and that
fact can be detected by the function boundp. The object contained in
the value cell of a bound symbol is the value of the global variable
named by that symbol, and can be accessed by the function
symbol-value. A symbol can be made to be unbound by the function
makunbound."

Symbol-value [2] accesses a symbol's value attribute, and it's
explicitly mentioned that unbound issues only occur on reads:
"Should signal unbound-variable if symbol is unbound and an attempt is
made to read its value. (No such error is signaled on an attempt to
write its value.) "
I'd think, then, that as long as some symbol-value is written first,
reading shouldn't be a problem.

The issue with symbol-macros and special variables still stands of
course.  But I don't think that a symbol needs to be declared as a
special variable in order for its symbol-value to be set and read.

//JT

[1] http://www.lispworks.com/documentation/HyperSpec/Body/t_symbol.htm#symbol
[2] http://www.lispworks.com/documentation/HyperSpec/Body/f_symb_5.htm#symbol-value

-- 
Joshua Taylor, http://www.cs.rpi.edu/~tayloj/